If the buzzer means “Emergency - a couple hundred lives in your care might be in jeopardy” I think the time would be well under a minute and a half.
A recent example: I stayed up a bit late on Wednesday, and so overslept on Thursday. I was expecting a somewhat important phone call from England, and woke to hear my cellphone (located in my kitchen) ring. I was able to take the call on the 5th (which is sometimes the last) ring.
I certainly wasn’t fully dressed. I question whether the AF447 captain was undressed and fully asleep. This source says he left the cockpit around 2:02, and the first call for him to return came at 2:10:50 - just 9 minutes later. And I question whether the A-330 has actual beds for pilots - a common arrangement is that a crew member can relax in a reclining seat and perhaps doze off, but he’s not in bed in his PJs.
That link also says that prior to the captain leaving the cockpit, there was a discussion about turbulence:
In view of this, leaving the cockpit itself may have been questionable. Leaving under the assumption that he should now expect a couple hours of uninterrupted sleep would have been a very dubious thing.
The OP’s link has this: “The co-pilot in the right-hand seat, an inexperienced 32-year-old named Pierre-Cédric Bonin…” … which sound like a junior pilot, in the sense of young, inexperienced, the opposite of “senior”.